1. Field of the Invention
The present invention relates to a phosphor layer for an image display apparatus, and in particular to a phosphor layer formation method for obtaining a high luminance and coating characteristic.
2. Description of the Background Art
In a conventional image display apparatus, energy is transferred to a phosphor surface formed on a panel 1 from an electron gun or a current generation apparatus in an amount which is capable of causing light to be emitted from a phosphor material thereby reproducing an image.
To form the phosphor surface, a phosphor material slurry is coated on the upper surface of the panel 1, and R, G, B phosphor material dots are formed on the panel by an ultraviolet ray exposure. Smaller phosphor material is used for the phosphor material slurry for enhancing a coating and filling characteristic of the coating surface. In addition, the shape of the phosphor layer is oval-shaped and hexagonal. The above-described phosphor layer has an aspect ratio (=shorter axis/longer axis) of 0.5xcx9c0.75.
The PVA (Polyvinyl Alcohol) phosphor slurry coated on the upper surface of the panel 1 is selectively exposed to ultraviolet rays, and the non-exposed slurry is removed by pressurized water for reproducing spotlights or dots or phosphor material on panel 1. During the light exposure, the ultraviolet ray should pass through the panel 1 for thereby coupling the PVA for thereby enhancing an adhesive force between the panel 1 and the dots. Namely, the adhesive force between the panel 1 and the dots of the phosphor is enhanced by increasing the light transitivity.
However, in the conventional phosphor layer (which is oval-shaped and hexagonal), the packing structure is too tight based on a constant light exposing amount as shown in FIG. 2, so that the light transitivity is decreased. In addition, some of the ultraviolet does not transmit to the inner portion of the phosphor layer and the panel 1, so that some of the adhesive force between the panel 1 and the dots is decreased. Therefore, cracks occur, and the coated state is degraded, and the luminance is decreased.
In order to overcome the above-described problems, in order to increase the light transitivity, the light intensity can be increased, or the light exposing time can be increased, so that the dot width is increased, but as a result a color mixing problem can occur.
In addition, the distribution of the conventional phosphor particle size has a Gaussian distribution due to the manufacturing characteristic. FIG. 1 illustrates a distribution by adapting a phosphor material having an average particle size of 6.5 xcexcm.
In FIG. 1, the sum of the volume of the particles in which the size of the particle starts 0 is 50% as d50 is assumed as d50. This value is an average particle size. The Quartile Deviation (Q.D.) is a parameter representing a degree of uniform distribution of particle size based on average size. The values Q and D are (d75xe2x88x92d25)/(d75+d25), and the distribution of the particle size becomes a reference for the uniform distribution based on the average size.
Here, the particle size distribution of the conventional phosphor material, in which the average particle size (d50) is 6.5 xcexcm, is 5% for each below 3 xcexcm and above 12 xcexcm, and the Q.D=(d75xe2x88x92d25)/(d75+d25) value is below 0.22. Therefore, the amount of elementary particles and alleles is too large, so that the packing structure of the phosphor material becomes compacted, so that the light transitivity is decreased. The phosphor is formed using the particles of 1xcx9c5 xcexcm, the packing structure of the phosphor becomes compacted, so that when an electron beam penetrates during the light exposure of the ultraviolet ray and when the phosphor material emits light, the particles does not penetrate into the lower surface for thereby decreasing the luminance.
In addition, the elementary particle phosphor material has a rapid luminance variation due to the variation of a film thickness, so that it is impossible to obtain an optimum film thickness which has the maximum luminance. In the fabrication line, in order to prevent any cracks of the phosphor material dots, the density of the phosphor slurry is increased, and the viscosity of the same is decreased. Therefore, a mixing problem may occur, and a filling problem may occur. In addition, the luminance may be decreased because the optimum film thickness of the phosphor surface is not obtained.
Accordingly, it is an object of the present invention to provide a method for manufacturing a phosphor layer for an image display apparatus which is capable of obtaining good coating characteristic and enhancing a luminance.
To achieve the above object, there is provided a phosphor surface formation method for an image display apparatus which is characterized in that a rounded phosphor material having an aspect ratio (=shorter axis/longer axis) of 0.8xcx9c1.0 is used as a phosphor material, and an average particle size (d50 the particle size in which the volume of the whole particles is 50%) is in a range of 1xcx9c8 xcexcm for thereby forming a phosphor surface wherein the phosphor surface is formed by manufacturing a phosphor slurry including a phosphor material, coating the phosphor slurry on an upper surface of the panel, light-exposing the same using ultraviolet rays, and removing a non-exposed portion by developing using pressurized pure water.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.